Idiopathic hypertrophic subaortic stenosis is being identified with increasing frequency in older patients. The results of operative treatment in 20 patients with hypertrophic cardiomyopathy 65 years of age or older, are described. All 20 patients were severely symptomatic prior to operation. Seventeen of the 20 patients had marked left ventricular outflow tract obstruction under basal conditions (average gradient 107 mm Hg); the other three patients had outflow gradients of greater than 50 mm Hg only with provocation.